Normally, a drive shaft (on a tractor, for example) and the end yoke of a transmission shaft are coupled via a transverse locking-pin, which, once connected, is uneven in shape and has projections that constitute a danger to anyone approaching the shaft whilst it is rotating, unless it is fitted with some form of protective casing.
Several types of protective casing have been designed to avoid this danger. According to one particularly simple kind of protective casing, the end yoke and locking pin are covered by a cowling attached to the machine from which the drive shaft projects. This, however, has considerable disadvantages, due, for example, to the fact that it requires holes being made in the machine in suitable positions so that the protective cowling can be attached. Moreover, the locking pin is very difficult to reach and requires the cowling being bent.
A type of protective casing is described in Patent GB-B-2102526 (corresponding to U.S. Pat. No. 4,501,573) which includes two half-casings that couple in such a way as to cover the locking pin, and rotate with the drive shaft. A conical casing covers these two half-casings and the yoke on the relevant joint. This system is rather complicated to unlock. In fact the casing has to be dismantled before the shaft can be disconnected by removing the locking pin.
A type of protective casing for the locking pin is known from Patent EP-B-O 201 464, (corresponding to U.S. Pat. No. 4,687,367), including a rotating sleeve that is internally provided with a specially shaped piece that moves the locking pin and thus disconnects the transmission shaft. This sleeve, which is attached to and turns with the transmission shaft, is highly practical in use as it covers the locking pin thus eliminating the uneveness and projections on the rotating shaft, and it also permits the transmission shaft to be disconnected without having to dismantle the protective casing. However, the amount of protection offered is limited, since the sleeve rotates with the shaft, i.e. it does not constitute a fixed protective casing.